The invention relates to a method and apparatus for winding a continuously advancing yarn to form a cross wound package.
In such a winding operation, the yarn is deposited at a crossing angle on the package surface within the package width at a substantially constant circumferential speed of the package. To this end, the yarn is reciprocated within a traverse stroke by a traversing yarn guide, before advancing onto the package surface. In this process, the length of the traverse stroke defines the package width.
A distinction can be made between two known methods of winding a package. In a first method, the traverse stroke is not varied in its maximum length during the winding cycle. With that, a cylindrical cross wound package is wound with substantially rectangular end faces. In so doing, the length of traverse stroke at the beginning of the winding cycle equals the length of the traverse stroke at the end of the winding cycle.
In the second method, the traverse stroke is constantly shortened during the winding cycle. In this instance, a cylindrical cross wound package is wound with oblique end faces. These so-called biconical packages thus slope relative to a normal plane, with the angle of slope being smaller than 90xc2x0. The traverse stroke at the end of the winding cycle has a length which is smaller than the length of the traverse stroke at the beginning of the, winding cycle.
Irrespective of which shape the end face of the package has, it is necessary to deposit the yarn layers at the ends of the package in such a manner that no irregularities develop by, for example, separating yarn lengths, such as the so-called yarn sloughs or slipping yarn layers. To this end, EP 0 235 557 and corresponding U.S. Pat. No. 4,913,363, propose to shorten and lengthen the traverse stroke cyclically during the winding cycle. This method is known as the so-called stroke modification. It permits producing a uniform mass distribution at the package edges, so that no beads form. Thus, while forming a straight end face, the length of the traverse stroke, which has been adjusted before the stroke modification, is again adjusted, after each modified stroke cycle. While winding a biconical package, a shortening of the basic traverse stroke defining the angle of slope, is adjusted after the modified stroke cycle.
DE 37 23 524 discloses a process wherein the end faces of a package are wound such that at the beginning of the winding cycle, a basic layer, which is wound at a smaller angle of slope, is initially built up. Subsequently, the winding cycle continues with a lesser shortening of the traverse stroke.
In practice, it has shown in the case of winding in particular textured yarns with a high crimp that, in particular in the center region of the package, beadlike bulges form at the end faces, which give rise to breakdowns at high unwinding speeds in the further processing.
It is therefore an object of the invention to provide a process of the initially described kind, as well as an apparatus for carrying out the method, which permits winding a cross wound package with substantially straight line end faces.
The invention distinguishes itself in that all overlying yarn layers of a cross wound package are included in the shaping of the end faces. The invention departs from the assumption that for producing a rectangular or a sloped end face of the package during the winding, the traverse stroke should be varied proportionately to the package width during the winding cycle. It has been found that the formation of the end face of the cross wound package is determined not only by the lengths of the traverse stroke, which are adjusted during the winding, but also results, after completion of the package, from the interaction of all overlying yarn layers. In this process, variations are found in particular in the intermediate diameter range of the package.
Such shape variations are taken into account by the method of the present invention, in that the lengths of the traverse stroke are varied during the winding cycle by a predetermined stroke function. The stroke function indicates the relationship between the winding, which may be defined by the winding time or the package diameter, and the lengths of the traverse stroke that are to be adjusted each time. In so doing, a certain length is associated in the course of the winding cycle to each traverse stroke by the stroke function, with the lengths of the traverse strokes being smaller than the respectively wound package widths. Thus, one may also consider the stroke function as a measure, which indicates the difference between the length of the traverse stroke and the final package width at the package diameter then being wound.
Especially advantageous for forming straight line end faces is a stroke function, in which a constant shortening of the traverse stroke relative to the package width is predetermined at the beginning of the winding cycle, and a constant lengthening of the traverse stroke relative to the package width is predetermined at the end of the winding cycle. Thus, the greatest deviations between the package width and the length of the traverse stroke result in the intermediate range.
The traverse stroke variations as are predetermined by the stroke function during the winding cycle are essentially dependent on one or more parameters, such as yarn tension, crimp of the yarn, yarn denier, package density, and yarn deposit, which is defined by the crossing angle and the yarn reversal. Thus, the relationship was found that, for example, a textured yarn with a relatively low crimp requires a stroke function which shows a greater deviation between the package width and the length of the traverse stroke in the intermediate range of the package. In comparison therewith, the winding of a package with a very high package density requires only a small deviation between the package width and the length of the traverse stroke.
In a particularly advantageous further development of the invention, a certain length of the traverse stroke is associated to each package diameter wound during the winding cycle. This permits producing and reproducing a very accurate geometrical form of the cross wound package.
In the case of cross wound packages, which are not subject to a preferred yarn guidance in the further processing, a variant of the method is advantageous wherein the stroke function effects on the end faces of the cross wound package a symmetrical shortening and a symmetrical lengthening of the traverse stroke. In this variant, both end faces of the cross wound packages are uniformly wound by the stroke function.
To facilitate as much as possible satisfactory unwinding properties of the yarn from a package being unwound overhead in a further processing step, it is preferred to use a variant wherein the stroke function effects an asymmetrical shortening and an asymmetrical lengthening of the traverse stroke. Thus both end faces maybe differently wound in their shaping.
Since a stroke function proceeds respectively from a maximum length of the traverse stroke adjusted at the beginning of the winding cycle and an end length of the traverse stroke adjusted at the end of the winding cycle, the stroke function is predetermined for an end diameter or an angle of slope. In particular, in the production of biconical packages, it will therefore be of advantage, when respectively one stroke function resulting in a certain angle of slope on at least one end face of the cross wound package, is associated to each wound end diameter of a c~ross wound package.
Likewise, in the winding of biconical packages, a variation of the angle of slope results in that the end length of the traverse stroke must be varied at the same time. To this end, it is especially advantageous to use a variant of the method wherein respectively one stroke function is associated to each angle of slope of the cross wound package. Each of the stroke functions is directed to a certain end diameter of the cross wound package.
In the winding of cross wound packages with an end face having an angle of 90xc2x0, the maximum length of the traverse stroke at the beginning of the winding cycle and the end length of the traverse stroke at the end of the winding cycle are each predetermined of an identical size. Contrary thereto, it is possible to adjust any desired angle of slope on the end face of the package by shortening the end length of the traverse stroke.
In a particularly advantageous variant of the method, the stroke function is input and stored in a controller. The controller connects to the drive of the traversing yarn guide, thereby influencing the traversing movement and the traverse stroke of the traversing yarn guide. For example, the stroke function could lead by means of a time program in the controller to a continuous and discontinuous variation of the traverse stroke.
To obtain an as precise as possible buildup of the package, a variant of the method is advantageous wherein the actual diameter of the package is continuously determined from the rotational speed of the package and the winding speed, so that the controller controls the drive with the length of the traverse stroke that is predetermined for the instantaneous package diameter.
The method of present invention is independent of the type of wind. The types of wind include random wind, precision wind, or stepped precision wind. In the case of the random wind, the mean value of the traversing speed remains substantially constant during the winding cycle. In this process, the wind ratio (spindle speed/traversing speed) varies continuously. In a precision wind, the wind ratio is kept constant. In a stepped precision wind, however, the wind ratio is varied in steps according to a predetermined program.
It is likewise very advantageous to combine the method of the present invention with the known ribbon breaking methods or with known stroke modification methods. With that, it is possible to produce cross wound packages with a large diameter and a great package length, which ensure a trouble free overhead unwinding of the yarn at high unwinding speeds of far above 1000 m/min.
The device of the present invention for carrying out the method distinguishes itself by a high flexibility in the production of packages. With its use it is easy to vary both the angles of slope in the case of biconical packages, and the end diameter of the packages.
When predetermining the traverse stroke, the controller proceeds each time from the instantaneous actual diameter of the package. To this end, the controller connects to a sensor that measures the rotational speed of the tube. One or more stroke functions are stored in a data storage. Likewise, the winding speed is stored as a known variable in the controller. By means of a computing unit, it is thus a possible to determine the instantaneous package diameter from the rotational speed of the tube and the winding speed. The stroke function, which associates with reference to a table of values, to each package diameter a certain, process optimized length of the traverse stroke, permits determining the length of the traverse stroke that is to be adjusted. With that, the drive of the traversing yarn guide is controlled with an optimal traverse stroke via the controller at any time of the winding cycle.
The flexibility of the device is further increased by the very advantageous embodiment of the invention wherein the traversing yarn guide is driven by means of a motor, in particular a stepping motor. With that, there exists the possibility of coupling the traversing speed with the respective length variation of the traverse stroke. A shortening of the traverse stroke can thus occur at a constant traversing speed or at a constantly deposited amount of yarn per unit time.
The coupling between the traversing yarn guide and the motor is advantageously provided in the form of a belt drive. To this end, the motor includes a drive pulley, which drives a belt extending over at least one belt pulley. The belt mounts the traversing yarn guide, and reciprocates it within the package width.
To obtain a uniform winding speed, it is advantageous to drive the tube or package by a drive roll in circumferential contact with the tube or the package. To this end, the tube is clamped in a package holder between two centering plates, with the sensor for measuring the rotational speed of the tube being arranged on the package holder.
In this connection, it will be especially advantageous, when the sensor is designed and constructed as a pulse transmitter. The pulse thus signals one revolution of the rotational speed as well as a zero position of the package. However, it is also possible to provide a plurality of markings on one of the centering plates, so that a plurality of pulses are signaled per revolution.
A further embodiment of the invention provides for the sensor signal to indicate not only the rotational speed of the package, but also the angular position of the package. This makes it possible to distribute the yarn reversal in the individual yarn layers evenly over the circumference of the package.